The present invention relates to vacuum transport devices, and more particularly, to a process and apparatus for transporting substrates between two regions having different pressures without substantially affecting the pressure of either region.
Semiconductor etching, cleaning, and deposition processes typically employ a plasma mediated process that is desirably carried out at a reduced pressure, e.g., in an evacuated (vacuum) chamber. It is important to maintain the pressure within the chamber within a specific predetermined range in order to avoid costly delays in the semiconductor wafer production process and to minimize undesirable variations in the quality of the semiconductor wafer products that are produced. Maintaining pressure within the predetermined range is difficult since, during device fabrication, substrates are sequentially fed into the processing chamber in a continuous or batch process from an external source operating at atmospheric conditions. Time spent controlling and readjusting the chamber pressure for each substrate or substrate batch introduced into the processing chamber can greatly increase processing times. The decreased throughput resulting from controlling and readjusting the pressure increases overall device costs. Chamber overhead time is defined as the time required for any operation involving the process chamber that does not include actual wafer processing time. The process chamber overhead time typically includes the time period for reducing the pressure within the process chamber to the desired processing pressure after each wafer exchange, heating the wafer to the desired temperature, venting the process chamber to allow wafer exchange and the wafer exchange itself. Minimizing overhead time increases productivity and reduces overall device costs.
Numerous apparatuses and methods exist for transferring semiconductor wafers into or out of a process chamber for continuous treatment without disturbing or otherwise affecting chamber pressure. Many such devices teach the use of an airlock chamber, i.e., a loadlock chamber, in operative communication with the processing chamber. Such a loadlock chamber can be adjusted to match the operating pressure in the processing chamber, thereby allowing transfer of substrates into or out of the process chamber while also allowing the process chamber to maintain a relatively constant pressure. In these devices, robots are generally implemented as a single arm whose travel moves a wafer in a substantially linear manner. The arm translation path is configured such that a central axis of the wafer passes over or near a central robotic arm pivot. Such pivots are typically mounted in the center of the loadlock chamber due to physical size limitations imposed by robotic link arm design and associated link arm travel. As a result, these types of transfer mechanisms suffer from excessive internal chamber volume in the loadlock chamber assembly due to the required translating arm paths of the transfer mechanism. Moreover, since the primary or first pivot of the link arm is centrally located within the loadlock chamber, repair and access to the apparatus is difficult. Also, the prior art often uses a complex system of a timing belt and pulley arrangement coupled to a step motor drive output shaft, and a sleeve coupled to a first link arm axis, in order to effect rotation of the arms.
For example, U.S. Pat. No. 4,584,045 to Richards, discloses the use of a belt drive in a wafer positioning transport apparatus. A problem exists through the use of a spring in one of the arms of the transfer mechanism. As the belt wears or stretches, the spring extends the arm to keep the belt tight. This alters placement of the semiconductor wafer in the chamber. Wafer positioning devices necessarily must be very accurate in the positioning at all stages of operation of the device. Such wear, which alters placement, is undesirable.
In U.S. Pat. No. 4,728,252 to Lada, a complex wafer transport mechanism is disclosed. The device of this patent has one shaft sealed within another shaft, which rotates independently of the outer shaft. A complex seal mechanism inherently exposes the device to potential failure and fretting. Also, the device employs belts and requires two motors and two motor control circuits, with the attendant wire harness and the like. The complexity of this device makes it expensive. Moreover, the use of belts increases the potential for fretting or wear, producing contaminants. In addition, as the belts wear or stretch, they need to be replaced on a regular basis, both in order to maintain the accuracy of the operation of the device, as well as to keep the number of contaminating particulates down within the apparatus. Replacement of belts produces additional maintenance costs and undesirable down time for the system.
A wafer transport apparatus and process for transporting substrates between two regions having different pressures without substantially affecting the pressure of either region includes a loadlock chamber assembly coupled to a process chamber. The loadlock chamber assembly includes a loadlock chamber and a sub-chamber in communication with the load lock chamber. The loadlock chamber is coupled to the process chamber and includes a closable port there between.
The sub-chamber comprises a first robot arm having a primary pivot axis within the sub-chamber, wherein the first robot arm can move a substrate from a position approximately in a center of the loadlock chamber to a position outside the loadlock chamber. The first robot arm includes a first end effector for holding the substrate during transport between regions.
The first robot arm is mounted onto a rotatable shaft sleeve and comprises a first link arm including an elongated housing having a first end and a second end, wherein the first link arm comprises a first cam disposed within the housing and a first four bar link mechanism driven by the first cam. The first cam is fixedly coupled to a shaft mounted coaxially within the shaft sleeve, wherein the shaft defines the primary pivot axis of the robot arm. The first robot arm further includes a first translating arm pivotably connected to the second end of the first link arm and having a first end effector attached to an end of the translating arm, wherein rotation of the first link arm about the shaft engages the first four bar link mechanism with the first cam and pivotably moves the first translating arm about a secondary pivot axis. The link arm and the translating arm fit entirely within the sub-chamber.
The first four bar link mechanism includes a first cam follower coupled to the first cam, a first driver link coupled to the first cam follower, and a first rocker link coupled to both the first driver link and the first link arm. The first rocker link comprises a rocker arm and a spring, wherein the spring is coupled to the housing of the first link arm and the rocker arm, and wherein the rocker arm is adjustably coupled to the driver link.
In a preferred embodiment, the loadlock chamber assembly includes a second robot arm pivotable about the primary pivot axis. The first and second robot arms can pivot independently of each other and are capable of placing one substrate into the process chamber while simultaneously removing another substrate from the process chamber. The first and second robot arms fit entirely within the sub-chamber.
The loadlock chamber assembly further includes a first motor for moving the first and second arms vertically along the primary pivot axis, a second motor for pivoting the first robot arm about the primary pivot axis, and a third motor for pivoting the second robot arm about the primary pivot axis.
The process for transporting substrates between two regions having different pressures without substantially affecting the pressure of either region includes housing a first and second robot arm in the removable sub-chamber coupled to the loadlock chamber. The first and second arms include a primary pivot axis within the sub-chamber. An active wafer is processed in the process chamber at a predetermined operating pressure, wherein the process chamber is coupled to the loadlock chamber and includes a closable port. The active wafer is removed from the process chamber with the first robot arm and a first queued wafer is deposited into the process chamber with the second robot arm at the operating pressure of the process chamber. The port is closed and the first queued wafer is processed in the process chamber at the operating pressure while the loadlock chamber is simultaneously vented for receiving a second queued wafer from outside the loadlock chamber. The pressure in the loadlock chamber is then reduced to the operating pressure and the port opened. The first queued wafer (now processed) is removed from the process chamber with the first robot arm and the second queued wafer is deposited into the process chamber with the second arm.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed